William Hague has ruled out British military involvement in Syria and branded Labour "opportunistic" for opposing action.

Speaking on Sky News' Murnaghan programme the Foreign Secretary said "Parliament has spoken" and that it would be unrealistic to try once more to persuade MPs to support military force.

In the highly unlikely event of a second vote, Labour would have to "play a less partisan and less opportunistic role and be prepared to take yes for an answer in terms of the motions that we present to the House of Commons", Mr Hague said.

He said he thinks the opposition party has "some hard thinking to do" in relation to their approach.

"There is some serious concern in other capitals, not just across the Atlantic but in European capitals as well, about the position they (Labour) have taken in voting down a government motion (on Syria)," he said.

Mr Hague said they "must dust ourselves down from that defeat" and support other nations.

Image Caption:Mr Obama and Joe Biden discuss Syria

But he denied that the country's entire foreign policy in regard to Syria had been rejected in Thursday's vote and pledged to continue to support the country with humanitarian aid and work with allies.

On Saturday US President Barack Obama confirmed that he believes in the use of force following the alleged use of chemical weapons by President Bashar al Assad.

He has formally requested authorisation from Congress before any action begins which means there will be no strikes before members will return on September 9.

Mr Hague insisted relations between the US and the UK remain strong and said Britain will provide diplomatic and political support.

He said: "The United States are clear that the special relationship remains.

"They have been very good about the result of our vote and understand that we respect democratic procedures in our country and so equally we must respect theirs.

Video:Syrian Activist Speaks To Sky News

"We are not going to get involved in their congressional debate.

"But, we do believe this threat has to be confronted and if it is not confronted now the confrontation in the end will only be bigger."

The French interior minister Manuel Valls told a radio station on Sunday that France cannot act alone against Syria and will await the US decision.

The Syrian main opposition bloc said it was "disappointed" with Mr Obama's decision to wait for Congress but said it believed lawmakers would approve a strike.

Pope Francis has condemned the use of chemical weapons and announced he would lead a worldwide day of fasting and prayer for peace in Syria on September 7.